I have examined the mag(internalField(U)) and vector(internalField(U),0,0) and vector(mag(internalField(U)),0,0) but the error persists.whats true expression.im in doubt internalField(U) is vector of U or magnitude although think it should be vector.

I have examined the mag(internalField(U)) and vector(internalField(U),0,0) and vector(mag(internalField(U)),0,0) but the error persists.whats true expression.im in doubt internalField(U) is vector of U or magnitude although think it should be vector.

Classic example of overcomplicated expressions leading to a "forest for trees"-effect: gradient of a vector in surface normal direction is a .... vector. Now have a look at the gradientEpression

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